Southbend lathe is UNC 60 degree while Boxfod is Whitworth 55 degree though tpi is the same.
A built in thread is good in many ways as it reduces overhang.
Cut a piece of thickish cardboard to a taper spanning the rough sixe of the hole. Screw it in and it will be marked up with the tread spacings at the core diameter of the thread. Make a few adjustments and you know the parameters. Do a bit of googling and you know what the chuck is off. You can also use bits of soft wood, like balsa bits of wood with plasticine on them, a few brain cells helps too.
Edited By Bazyle on 26/04/2015 18:45:10